Warning: Spoilers!

Rishid was abandoned as a baby near the entrance to the underground home of the Gravekeepers.  He was found by the wife of the leader of the Gravekeepers, and she took him in as her own son.  She and her husband, surnamed Ishtar, had no children of their own, and she wanted to formally adopt him as the heir to the secrets of the gravekeepers if she had no children by the time he was ten.  That would mean that at that time he would go through the ritual scarification that would mark him as the next leader.  He overheard them talking about it one night and was overjoyed at the thought that he could be their real child, and be part of a real family.

When he was four or five, Isis was born.  His mother still wanted to adopt him as the heir, because a girl couldn't take over as the leader, but her husband wouldn't hear of it.  Despite this, as Rishid neared ten with no biological sons in sight, his mother prepared him for the possibility that he might be the heir.  He told her that he knew it would hurt and be hard, but that he wanted to go through it more than anything, because it meant he would be her real son.

Before he turned ten, Malik was born, and his mother died shortly after giving birth.  Rishid became the boy's surrogate mother, his only duty to take care of him.  As this gave him the possibility of acceptance by his only father figure, Rishid didn't mind.  Besides, he loved Malik.

When Malik was around five, he got bitten by a poisonous snake and was very sick.  His father told Rishid that if Malik died, he would too and that he should have been the one to get poisoned.  Rishid became enraged out of anger at his treatment and decided to kill Malik.  The only thing that stopped him was Malik calling him "brother" and saying that he always thought of him in that way.
When Malik neared ten and was terrified over the ritual, Rishid begged his father to let him undergo it in the younger boy's place.  He was violently refused, and had to stand by while the boy he had taken care of and protected for the past ten years was dragged by him, screaming.  Since that method of showing his family loyalty was denied him, Rishid took a knife and carved heiroglyphs into his face.  These acted as a seal to keep Yami Malik away from the surface of Malik's personality.  When Rishid loses consciousness, the seal breaks, and Yami Malik is able to come forth. 

This first happened a year after the ceremony.  The three children conspired to sneak Malik out of the underground home to see the sun and the nearby town with Isis, and Rishid would keep them covered at home. They were discovered while out, and their father beat Rishid mercilessly.  By the time they got home, he was barely conscious, and he passed out shortly after they reached the room he was being punished in.  Yami Malik was released, and he killed the senior Ishtar.  Before he could kill Rishid as well, the older boy came to and Yami Malik was pushed down again.  Malik had no memory of what he had just done, and believed Shadi when told that it was because of the pharaoh.  He ran away, determined to destroy the pharaoh, and Rishid went with him.

Malik had the Millennium Rod, which let him control people's minds, but he never needed to use it with Rishid because he trusted him.  During the course of the anime, he hits him with the Rod and insults him, but Rishid is always loyal to him.  His biggest wish is to help Malik get his wish, to protect him, and to prove his loyalty to his adopted people.